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Sniff ... Who Goes There?

Animals in the real world don't call each other by name like the ones in cartoons, so how do they tell who's who? By smell, according to those in the know. New research suggests that squirrels not only use their noses to tell relatives from strangers, but can discriminate degrees of relatedness. Researchers suggest that the odor ID system could help the squirrels decide who they'd risk their life for, and it could help them avoid inbreeding too.

If a Beldings squirrel notices a coyote skulking around outside its burrow, it sometimes sounds the alarm to alert its neighbors. Because a squirrel is twice as likely to become a meal if it whistles a warning, biologists have shown that it will only do so if the threatened squirrels are close relatives. This type of family favoritism--known as nepotism--exists in many species, including humans. Behavioral ecologist Jill Mateo wanted to find out if Beldings rely on scent to figure out who's in the family.

Mateo, a professor at Cornell University in Ithaca, New York, set up communities of Beldings squirrels in California's Sierra Nevada mountains using large wire enclosures full of buried tunnels and fabricated burrows. Over the last 5 years, she has tagged the squirrels and worked out who is related to whom. In the current study, she wiped small plastic cubes along the scent glands of certain animals and placed these in front of a burrow. The animal inside eventually came out to investigate.

After allowing a squirrel to get used to an unrelated "reference" animal's odor, Mateo tested whether the informed rodent could discern odors from the reference's kindred. The length of time the squirrel spent sniffing around the cube indicated how well it recognized the odor. The least time was devoted to the most familiar scents--those of the reference and its mother, followed by more distant relations such as aunts and grandmothers. Scents of strangers were sniffed the longest, Mateo reports in the 7 April issue of the Proceedings of the Royal Society B. "I was surprised at just how good they are," she says. Mateo also found that non-nepotistic golden squirrels can also identify kin through smell, suggesting that nepotism isn't the only application for the sniff test.

Although Beldings squirrels may use the system to save relatives from harm, the fact that it exists in species that don't play favorites suggests it arose for a more fundamental reason, such as avoiding inbreeding, says Wayne Potts, a molecular geneticist at the University of Utah, Salt Lake City. He says Mateo's attention to detail makes the study "the best demonstration that different degrees of relatedness can be discriminated [by smell]."